Scanning probe in pulsed-force mode, digital and in real time

ABSTRACT

A microscope, in particular a scanning probe microscope, comprising a programmable logic device.

CLAIM OF PRIORITY

This application is a continuation of and claims priority fromapplication Ser. No. 11/584,843, which is a continuation of and claimspriority from application Ser. No. 10/433,917 filed Dec. 1, 2003, whichis a §371 of PCT/EP01/14593 filed Dec. 12, 2001, designating the UnitedStates of America and from which priority is claimed, and which in turnclaims the benefit of priority under 35 U.S.C. §119 of German PatentApplications Serial Nos. 100 62 049.3, filed on Dec. 13, 2000, and 102005 055 460.1, filed on Nov. 22, 2005. This application also claims thebenefit under 35 U.S.C §.119(e) of U.S. Provisional Patent ApplicationSer. No. 60/738,903, filed on Nov. 22, 2005.

BACKGROUND ART

The invention relates to a method for producing the image of a surfaceof a specimen to be examined with a resolution which is better than 1 pmlaterally to the surface and better than 100 nm perpendicularly to thesurface, with a scanning probe scanning the surface point by point andthe distance between the scanning probe and the specimen surface beingmodulated at each scanning point, thus leading to a force-time curve.The invention also provides a scanning probe microscope for performingsuch a method.

A large number of methods for imaging the surfaces of specimen pieces bymeans of scanning probes have already been described in the state of theart.

One possibility for examining a specimen surface and for producing asurface image by means of a scanning probe is that the scanning probe isbrought into contact with the surface of the specimen and the surface ofthe specimen is then scanned. Such an imaging method is known as“contact-mode” and is used for example for determining the topographyand the local friction. With respect to the “contact-mode method”,reference is hereby made to the following publications:

-   -   Maivald P, Butt H-J, Gould S A C, Prater C B, Drake B, Gurley J        A, Elings V B and Hansma P K (1991), Using force modulation to        image surface elasticities with the atomic force microscope,        Nanotechnology, 2, 103-105, and    -   Marti O and Colchero J, 1992, “Reibungsmikroskopie” (Frictional        Microscopy), “Phys. Rafter” 48, 107,        the disclosure of which shall both be fully included in the        present application by reference.

The disadvantage of this imaging method is that when moving the scanningprobe which is in contact with the surface of the specimen piece,shearing forces will occur which deform the surface of soft specimenssuch as polymeric or biological systems or can even destroy the same.

In order to protect a surface from deformation or destruction it isadvantageous to examine the specimen surface with the help of a methodin which the scanning probe is not in contact with the same. This methodis generally known in literature as “non-contact mode”. It is a methodwith which a destruction of the specimen surface can be excludedentirely. One disadvantage of this method is however that the resolutiondecreases with increasing distance between scanning probe and specimensurface and no mechanical specimen properties can be examined.

Reference is hereby made with respect to the “non-contact mode”, thedisclosure of which are both hereby fully included in the presentapplication by reference:

-   -   Martin Y, Williams C C and Wickramsinghe H G. (1987), Atomic        force microscope-force mapping and profiling on a sub 100-A        scale, J. App. Phys., 61, 4723;    -   Sarid D, Ruskell T G, Workman R K and Chen D, 1996, J. Vac. Sci.        Technol. B, 14, 864-7.

A method which allows the examination of soft specimen surfaces such asthose of polymers but which on the other hand still offers sufficientinformation on the specimen surface is the so-called“intermediate-contact-mode” method, in which a scanning probe can bemade to oscillate close to its natural frequency. The oscillatingscanning probe is moved towards the specimen until it touches thespecimen surface. The phase shift between the free oscillation in airand the oscillation when the scanning probe approaches the surfacedepends on the elastic-viscous properties of the probe and the adhesivepotential between specimen and scanning probe. In this way it ispossible to determine the elastic properties.

Reference is hereby made with respect to the “intermediate-contact-mode”method to the following:

-   -   Spatz J, Sheiko S, -Moller M, Winkler R, Reineker P and Marti 0,        (1995), Forces affecting the substrate in the resonant tapping        force microscopy, Nanotechnology, 6, 40-44;    -   Digital Instruments, Incorporated, U.S. Pat. No. 5,412,980        (1995), Tapping atomic force microscope;    -   Digital Instruments, Incorporated, U.S. Pat. No. 5,519,212        (1996), Tapping atomic force microscope with phase or frequency        detection,        which disclosures are hereby fully included in the present        application by reference.

The “intermediate-contact-mode” method comes with the disadvantage thatthe two variables, amplitude and phase shift, depend on a plurality ofvariables, so that a simple allocation to a physical variable is notpossible.

These disadvantages can be overcome in such a way that the entireforce-path or force-time curve is absorbed when the scanning probeapproaches the specimen surface. This curve comprises the entireinformation of the interaction forces between scanning probe andspecimen and allows a precise definition of the elastic-viscousproperties and the adhesive forces.

Concerning this method reference is hereby made to:

-   -   Radmacher M, Cleveland J P, Fritz M, Hansma H G and Hansma P        K, (1994) Mapping interaction forces with the atomic force        microscope, Biophys. J, 66, 2159-65;    -   Radmacher M, Fritz M, Cleveland J P, Walters D A and Hansma P K,        (1994 Imaging adhesion forces and elasticity of lysozyme        adsorbed on mica with the atomic force microscope, Langmuir 10,        3809-14;    -   Van der Werf K 0, Putman C A J, Groth B G and Greve J (1994),        Adhesion force imaging in air and liquid by adhesion mode atomic        force microscopy, Appl. Phys. Left, 65, 1195-7;    -   Mizes H A, Loh K-G, Miller R J D, Ahujy S K and Grabowskie E F        (1991), Submicron probe of polymer adhesion with atomic force        microscopy; dependence on topography and material        inhomogeneities, Appl. Phys. Lett. 59, 2901-3        Which disclosures are hereby fully included in the present        application by reference.

The disadvantageous aspect in this method is that the scanning speed forrecording an image is very low.

In order to increase this speed a new method was developed, theso-called “pulsed-force-mode” microscopy. In “pulsed-force-mode” (PFM)microscopy, the scanning probe is made to oscillate periodically in thez direction, i.e. the perpendicular direction relative to the specimensurface, and the force-time curve, which is an image of the force-pathcurve, is recorded and certain parameters of this force-time curve areevaluated with the help of analog circuits such as trigger circuits inorder to obtain an image of the specimen surface.

Concerning the “pulsed-force-mode” microscopy reference is hereby madeto:

-   -   Rosa A, Weiland E, Hild S and Marti O, The simultaneous        measurement of elastic, electrostatic and adhesive properties by        scanning force microscopy; “pulsed-force-mode-operation”. Meas.        Sci. Technol. 8, (1997), 1-6        whose disclosure is fully included in the present application by        reference.

The disadvantageous aspect in the imaging method of a specimen with thehelp of the “pulsed-force” microscopy as has become known from the stateof the art, e.g. through the above document, is that triggers need to beplaced for processing the analog signals. Since the evaluation of thepulsed-force curve is substantially limited to the time of theoccurrence of the triggers, this leads to inaccuracies and optimalsignals can only be obtained with difficulty.

Moreover, the setting of the triggers requires skilled staff and is verytime-consuming.

A further disadvantage in the “pulsed-force” microscopy according to thecurrent state of the art is that the possibilities for evaluating theforce curves is very limited and thus remain inaccurate. As a result, itis possible to obtain quantitative measured values which are relevantfrom a viewpoint of material sciences only with much difficulty.

Moreover, the method is limited to a maximum of two variables which canbe evaluated per measurement made with scanning microscopy, which isoften inadequate.

Other embodiments of scanning probe microscope comprises at least oneperipheral electrical component, such as for instance a D/A or A/Dconverter and a programmable logic device. One particular programmablelogic device is a so-called programmable gate array (FPGA). Preferably,in the present invention the programmable logic device is developed asan FPGA.

The scanning probe microscope preferably serves to generate the image ofa surface of a sample being analyzed. In images of this kind theresolution can be better than 1 μm lateral to the surface and betterthan 100 mm perpendicular to the surface. The scanning probe scans thesurface point-by-point. In one application, which serves only as anexample and is not to be seen as limiting the scope of the invention inany way, the distance between the scanning probe and the sample surfaceis periodically modulated, such that for instance a force-time curveresults. This force-time curve can then be evaluated and the developmentof different surface parameters can be ascertained. A scanning probe canalso be an optical probe for directing light onto a surface to bescanned, for instance by means of a cantilever tip into which laserlight is coupled. With respect to near field scanning optical microscopyreference is made to U.S. Pat. No. 5,756,977, DE 19902235 A1 and DE19902234 A1. A further form of optical scanning probe microscopy isscanning probe Raman spectroscopy/microscopy.

Consequently, in the present application scanning probe microscopy isvery generally defined as a microscope whereby a sample surface isscanned point-by-point. Therefore, this definition of the scanning probemicroscope and scanning probe microscopy include for instance confocalmicroscopy, scanning force microscopy, scanning tunneling microscopy,optical near-field microscopy and also scanning electron microscopy.Accordingly, scanning probe microscopy is not restricted to scanningprobe microscopy involving a force-time curve being recorded with theaid of a scanning probe. Consequently, the description of the inventionfor a scanning probe microscope for recording force-time curves onlyserves to describe the invention better by means of an example, but inno way restricts the scope of the invention. Scanning probe microscopyfor recording force-time curves is just a preferred embodiment and isnot a restriction.

If in a scanning probe microscope as in the state of the art, theperipheral components are actually controlled by means of controllers ormicrocomputers via a data bus system, such a transfer of data by meansof a bus system has numerous disadvantages.

As the controllers or the digital signal processors (DSP) control theperipheral devices, such as for instance the D/A converters, the A/Dconverters or the digital input and output devices via a bus or aplurality of buses, developed as multi-drop buses, these must beprovided with electronic digital technology for controlling access tothe bus of for instance the controller or the microprocessor and fordecoding the requests from the microcontroller or the digital signalprocessor. In addition, synchronizing the analog/digital convertersand/or the digital/analog converters and the digital input and outputdevices requires further logic components in order for instance tosynchronize a scanning movement involving the simultaneous movement ofmore than one channel and to simultaneously measure the values for eachscanning point. Furthermore, the circuits require complex terminals tomaintain the integrity of the data.

WO2004/057303 makes known a controller for a scanning probe microscopethat employs a programmable logic device in the form of FPGAs. However,in WO2004/057303 it is not the entire programmable logic control unitthat is developed as a programmable logic device, but just one part,namely the lock-in amplifier, developed in the programmable logic deviceas a digital two-phase lock-in amplifier. This fully digitalprogrammable logic lock-in amplifier is connected to a digital signalprocessor that, in turn, is part of the controller. The programmablelogic device in WO2004/057303 in the form of an FPGA is only anauxiliary component of the digital signal processor for signalprocessing and not the controller itself. Consequently, the signalprocessor in WO2004/057303 encompasses the scanning probe microscopecontroller for controlling the control circuits and the entire scanningprobe microscope scan and not the programmable logic. The digital signalprocessor communicates with all peripheral devices by means of amulti-drop bus.

A further disadvantage of these kinds of systems in accordance with thestate of the art is their inflexibility. If one wishes to add a newstate-of-the-art peripheral device to the system it is necessary tocalibrate the bus timing again as the additional data load resultingfrom the system automatically puts an extra load on the bus system. Thebottleneck caused by this bus system also constitutes a bottleneck forthe digital signal processor or the microcontroller as only one commandor just a few parallel commands can ever be executed in themicrocontroller or processor. Furthermore, every peripheral device in astate-of-the-art system with a multi-drop bus is constructed in a verycomplex manner as parts of the peripheral component are required toimplement the bus protocol used by the multi-drop bus, for instanceaddress decoding or bus arbitration. Furthermore, circuit terminationfor more than two circuits for a bus system is very complex andelaborate.

SUMMARY OF THE INVENTION

Consequently, an object of the invention is to overcome thedisadvantages of the state of the art and provide a scanning probemicroscope that features rapid data collection, data processing and highflexibility.

In accordance with the invention this object is achieved by means of amicroscope, in particular a scanning probe microscope, where at leasttwo peripheral devices are linked directly with a programmable logicdevice without the interconnection of a multi-drop bus.

With respect to programmable logic reference is made to:

-   -   Ashok K. Sharma: “Programmable Logic Handbook: PLDs, CPLDs and        FPGAs (McGraw-Hill 5 Professional Publishing; ISBN: 0070578524)”        or;    -   W. Bolton, Bill Bolton: “Programmable Logic Controllers: An        Introduction” (Butterworth-Heinemann; ISBN: 0750647469).

A programmable logic device comprises a large number of logic componentsand/or logic elements and/or logic switches, such as for instance ANDgates, OR gates, flip-flops or memory elements. The single logiccomponents can be interconnected using a netlist and by means of freelyconfigurable circuits in accordance with a circuit diagram. In contrastto AISEC modules, this interconnection is not permanent, but can bemodified at any time using the netlist. Free configurability requires ahigh degree of flexibility. The logic components are interconnectedusing activated transistors that are activated in accordance with thenetlist, which is a representation of the circuit diagram. Completemicroprocessors or digital signal processors (CUSP) can be representedin programmable logic with the aid of appropriate logic componentinterconnections. These are known as softcores or IP soft cores. It isalso possible to integrate hardware processors or digital signalprocessors into a programmable logic device. Hardwired processors ordigital signal processors are also known as hard IP cores.

A structure of this kind provides the scanning probe microscope withgreat flexibility as the central control unit of the system inaccordance with the invention is developed as a programmable logicdevice. Consequently, when a peripheral component is added or exchanged,only the programmable logic has to be reconfigured using the netlist,not the hardwired architecture of the system. It is no longer necessaryto calibrate the peripheral components to match the bus architecture. Incomparison with bus architecture, one is far more able to interface theindividual peripheral components directly with the programmable logicdevice using a star topology. The star circuitry allows the peripheralcomponents with extreme data transmission rates in excess of 100 kHz tobe driven and controlled in parallel mode. Consequently, digital log-inamplifiers for instance can be developed in the range of several MHz.While the control response time for previous systems was in the range ofits, thanks to the use of programmable logic in the system in accordancewith the invention this lies in the range of ns. This makes it possiblefor instance to count individual photons, such that the apparatus inaccordance with the invention can be employed for instance in confocalmicroscopy, i.e., in optical scanning probe systems with timeresolution.

For the first time, this invention makes it possible to develop acontroller as a system on a chip or even on a programmable chip. In thismanner, a star topology can be developed which simplifies routingconsiderably in comparison with systems in accordance with the state ofthe art employing a bus. Furthermore, the noiselessness of theconverters and electromagnetic compatibility is improved. Elaborateterminals such as for multi-drop busses are no longer required. Thesystem can be easily expanded as no address decoding or arbitrationlogic is required. Timing behavior is totally deterministic.

Using the scanning probe microscope in accordance with the inventionemploying programmable logic, where the controller is also representedin the programmable logic device, it is possible to control the probemovement in 2 or 3 dimensions, to measure quantities such as forinstance light intensity, photon numbers, electrical currents anddifferentials and mechanical quantities such as for instance forces,deformation, oscillation amplitudes and phases, positions, and spectraduring probe movement, and to control these with reference to setvalues. Furthermore, various switches, relays, stepper or DC motors,cameras, luminaries, shutters, folding mirrors, electrical voltages forcombined experiments and the like can also be controlled. Analogcrosspoints are no longer required to control the different switches,relays, stepper or DC motors etc. Instead, a multiplexer developedwithin the programmable logic device can be employed.

In controlling probe movement, parallel control of the axes of thescanning probe microscope is possible, that is along the two axes on theX-Y plane and also along the Z axis, along which height data isobtained.

The parallel control of scan movement and closed-loop feedback providessmoother movement than in comparison with the state of the art as acentral processing unit does not need to switch back and forth betweenvarious tasks.

Furthermore, it is also possible to synchronize external devices, suchas CCD cameras, with the scanning. A further advantage of the system isits simple maintenance.

Consequently, as the complete system is developed as a programmablelogic device, it is possible in many cases to carry out maintenancetasks on the customer's premises solely by accessing the netlist bymeans of software, as the netlist defines the programmed logiccircuitry.

Furthermore, so-called EMC behavior is improved with respect not only tothe electromagnetic radiation, but also to the noise immunity as most ofthe data processing, in particular the high frequency digital dataprocessing in the programmable logic device, developed as an FPGA chip,takes place at very low voltages between 1.2 Volt and 1.5 Volt. As thenumber of external digital circuits is restricted to a minimum, thesignal/noise ratio of the analog inputs and outputs is also improved.Preferably, the programmable logic device and/or the field programmablegate arrays (FPGA) or a programmable logic device employing an embeddedCPU, a programmable logic device employing an embedded microcontrolleror a programmable logic device with a digital signal processor is/areinterconnected by means of netlists, such that the programmable logicdevice processes all the parallel tasks simultaneously.

Thanks to its open configurability, the scanning probe microscopedescribed here with its programmable logic offers the advantage that thescanning probe microscope can be provided with new or extendedfunctionality, without modifications to the hardwired electronics. Thescanning probe microscope is developed as a system on a programmablechip.

Reconfiguration is for instance possible using a microcomputer by meansof a modified netlist within a few seconds. This makes it possible forinstance to add new, faster components in a simple manner.

To do so, the netlist only needs to be modified with respect to thecorresponding logic.

Within the scope of the present application, interfaces are alsoperipheral devices. Examples of interfaces are the RS232 interface, theIEEE interface, the TCP/IP interface, the Ethernet interface or a USBinterface. The aforementioned interfaces are connected directly to theprogrammable logic device without the interconnection of a data bus.

In a first embodiment in accordance with the invention, the scanningprobe microscope comprises one or a plurality of A/D converters, one ora plurality of D/A converters, and one or a plurality of digitalinput/output terminals.

Preferably, the A/D converters have a width of 14 bit or more, forinstance 16 bit, and a clock speed in excess of 100 ksamples/s,preferably in excess of 1 Msamples/s or more than 5 Msamples/s.Preferably, each measurement wire and/or control wire has its owndesignated A/D converter. There is then no longer any need for an analogmultiplexer, which reads in measured data from a plurality of datachannels and transmits these to a single A/D converter. By dispensingwith the analog multiplexer the signal-noise ratio for the individualdata channels is improved and crosstalk between various data channelsprevented.

In one particularly preferred embodiment the device comprises at leastfive analog/digital converters. Preferably, the number of D/A convertersexceeds four. The D/A converters are provided with a width of 14 bit ormore and also a sampling rate in excess of 100 ksamples/s, preferably inexcess of 5 Msamples/s, preferably 50 Msamples/s.

In one preferred embodiment the scanning probe microscope is providedwith three D/A converters, with one D/A converter generating an offseton one analog output and the second D/A converter generating thereference voltage for the third D/A converter and the analog addition ofthe outputs from the first and third converters constituting the actualanalog output. Highly preferable is when the D/A converters of ascanning probe microscope can be digitally controlled by a programmablelogic device and one or a plurality of closed loop control systems canbe developed using A/D converters and D/A converters. In particular, itis an advantage when a positioning device for positioning and scanningcan be actuated and/or controlled in one, two or three dimensions.

The digital input and output interface can be provided by means of a TTLwire, an RS232 interface, a 12C interface, an Ethernet interface or aUSB interface. The input/output interface (DIO) and/or the outputinterface (DO) in one preferred embodiment of the invention can serve tocontrol stepper motors, folding mirrors, filter wheels, filter sliders,lasers, shutters, spectrometers, spectrographs, counters, on/offswitches, CCD cameras and scanning systems and/or read in or read outdata from these systems. The interfaces can also be interfaces thatcreate connections to peripheral devices, developed as microcomputers ordigital signal processors. A connection of this kind can be made bymeans of an Ethernet, CCP/IP, USS or an interface with data bufferingemploying FIFO. The data transfer rate exceeds 10 Mbytes, preferablyabove 20 Mbytes. A connection to other programmable logic networks isalso possible.

The invention can be employed in every type of microscope, in particularin a scanning probe microscope, in particular also in a scanning forcemicroscope, a scanning tunneling microscope, a near-field scanningoptical microscope, a confocal laser scanning microscope, a confocalscanning microscope, a confocal Raman scanning microscope, a photonicforce microscope or a scanning electron microscope. A scanning probemicroscope in accordance with the invention can for instance be employedfor recording and evaluating force distance curves.

A microscope of this kind will be described subsequently purely as anexample that in no way limits the scope of the invention.

Force distance curves can be used to separately measure diverse sampleparameters with a single measurement, such as for instance viscous,adhesive and elastic behavior. As the force distance curves are fullyavailable in digital form at the end of a measurement and thereforeavailable for post-processing if required, the stored data are alsoavailable for subsequent analysis of measurement artifacts.

In one embodiment of the invention the frequency of the periodicmovement of the scanning probe for recording force distance curves inthe direction perpendicular to the sample surface 1 Hz to 20 kHz and theamplitude ties within the range of 10 to 500 nm. More advantageously,sinusoidal or similarly shaped forms of excitation are selected, butother forms of excitation such as sawtooth or trapezoidal can also beadvantageous. An analysis of the actual movement of the scanning probemakes it possible to modify or change the form of the excitation in sucha manner that the probe executes the desired periodic movement.

The force distance curves can be used to determine the characteristicquantity, for instance the maximum repulsive force value from thedigitized force-time curve that results while the scanning probe is incontact with the surface.

A further characteristic quantity that can be determined is thedifference between one point in the rising or falling branch of theforce-time curve in relation to maximum force. This difference is then aquantifiable measure of the local stiffness of the sample and offers astiffness image of the surface when entered on the scanned area.

A further characteristic quantity from the force-time curve is theminimum attractive force while the tip is detaching from the samplesurface. This characteristic value is a quantifiable measure for thelocal adhesion of the sample and produces an adhesion image of thesurface when it is entered over the scanned region. A furthercharacteristic quantity that can be determined is the minimum forcevalue when the sample probe snaps onto the sample surface. This minimumforce value is a quantifiable measure of the local attraction of thesample. If this characteristic quantity is entered over the scannedregion, an attraction image of the sample can be obtained. Stiffnessimages of the sample can also be determined in another manner from therecorded force-time curve. In a first embodiment, a stiffness image isobtained in such a way that the slope of the force-time curve at acertain time when pressing the sample probe into the sample surface isdetermined as a characteristic quantity. This slope is a quantifiablemeasure of the local stiffness of the sample.

As an alternative to this, the slope can be determined at a specificrelative time of the force-time curve when the sample probe is retractedfrom the sample. This slope is also a quantifiable measure for the localstiffness of the sample and results in a stiffness image of the samewhen entered over the scanned region.

A further characteristic quantity is the frequency of the freeoscillation of the cantilever. This quantity is a quantifiable measurefor the collected impurities or damage to the tip.

A further characteristic quantity of the digitized force-time curve isthe ratio between the minimum force value when detaching from the samplesurface and the measured force value at the first subsequent local forcemaximum. This characteristic value is a quantifiable measure for theenergy dissipation when detaching the tip from the sample.

If one determines the rise time from the beginning of the contact untilthe maximum force from the force-time curve, it is possible to generatea rise time image of the sample surface. Employing an analogous methodit is possible to obtain a fall time image of the sample surface bydetermining the fall time from the digitized force-time curve.Furthermore, the time of the repulsive contact between sample and tip orthe time of contact between sample and tip can be determined from thedigitized force-time curve. When entered over the scanned region, thesetimes lead to a repulsive contact image or a contact time image of thesample surface. In a similar manner as for the contact periods in therepulsive region of the force curve, a refined embodiment of theinvention provides for contact periods for the adhesive section of theforce curve to be determined, for instance from the force minimum to thezero crossing of the force curve.

When entered on the scanned region, these periods generate acontact-breaking period image of the sample surface.

In addition to the direct evaluation of the force-time curve, it ispossible to determine various integrals under the force-time curve ascharacteristic quantities. For example, it is possible on the basis ofthe digitized curve to determine the integral under the force-time curvein the region of the repulsive contact or from the beginning of thecontact until reaching the maximum force and from reaching the maximumforce until the zero crossing of the force. When entered over thescanned region, these integral values offer a repulsive contact integralimage of the sample; in the case of the integral from the beginning ofthe contact until reaching the maximum force, an image of the workexerted on the sample and in the case of the integral from the time ofreaching the maximum force until the zero crossing, an image of the workprovided by the sample.

Similar to the integrals in the repulsive region, integrals for theadhesive region of the force curve can also be determined from thedigitized force-time curves. It is possible for instance to determinethe area under the force curve from the time of minimum force until thetime of the zero crossing of the force curve. This integral is a measurefor the local viscoelastic properties of the sample.

If one calculates the difference between the integrals in the region ofthe repulsive contact and the integral under the force-time curve fromthe beginning of contact until reaching the maximum force, an image canbe produced of the work dissipated in the sample.

One or a plurality of the obtained evaluation results can be used as acontrol signal for tracking the scanning probe on the sample topographyor for controlling the modulation signal. Preferably, the differencebetween the maximum repulsive force value and the force value obtainedwhen the scanning probe is close to but not yet I\in contact with thesample is usually used as the control signal for tracking the scanningprobe on the sample topography. It is also advantageous and possible touse other quantities.

If the digitized force-time curves are stored in a memory area, certainvariables of the force-time curve can be determined by post-processing.The quantities as described above, that is the force-time curve and eachposition of the sampling platform and the force-time curve data, can bestored with temporal information. This is known as a timestamp. If thequantities are stored with this timestamp, for instance in a memory areaof the FPGA, a parametric representation of the complete scanningmeasurement results. In prior systems, the sampling platform was forinstance brought into a certain position, a spectrum recorded at thisposition, for instance using scanning Raman microscopy with the aid of aCCD camera, the recorded data was stored, and the sampling platform thenbrought into a second position. If, on the other hand, the position ofthe sampling platform is given a timestamp, as are the measurement data,the positional displacement of the sampling platform and the measurementdata from for instance the CCD camera, can be recorded continuously andindependently of each other. The timestamp allows the data to becorrelated in any way, it is no longer necessary to have a trigger aswas the case in prior systems, for instance displacing the samplingplatform and recording the measurement data. This significantlyaccelerates the recording of measurement data. Furthermore, differentviews can be calculated from the stored data. As described above, it isno longer absolutely necessary to synchronize the data on the hardwareside thanks to the timestamp, as it can be produced at any subsequenttime in the software. Consequently, using this method it is alsopossible to distort the image based on a specified position using theactual measured position. In the scanning probe microscope describedabove for recording force-time curves, it is advantageous for theoscillating movement of the scanning probe perpendicular to the samplesurface to be excited with the help of a piezoelectric element,Alternatively, provision can be made for the scanning probe to comprisea tip arranged on a beam and the means for recording the force-timecurve and means for measuring the beam deflection, for instance with theaid of the deflection of a laser beam. The deflection of the laser beamis preferably measured using a quadrant detector or a position-sensitivephotodiode. The invention is described below with reference to thedrawings.

It is a further object of the present invention to provide an imagingmethod for an apparatus comprising a scanning probe which allows on theone hand recording a plurality of physical properties bothquantitatively as well as qualitatively during a measurement made with ascanning microscope and provides on the other hand an image in a shortperiod of time and with sufficient precision.

The invention shall also enable for the first time more complexvariables such as constant maximum force (by taking into accountmeasurement artifacts produced by interference or long-range forces forexample), constant energy supply, constant penetration depth, etc. orcombinations of such variables for control. The change between differentcontrol parameters should be possible. In order to make all parameterscontained in the force-time curves accessible for the measurement and toincrease the measurement precision in a number of material parameters,the invention shall further allow an active control of signal shape,phase, frequency and amplitude of the modulation signal.

This object is achieved in accordance with the invention in such a waythat in the case of a method according to the preamble of claim 1 theforce-time curve recorded with the help of the pulsed-force mode isdigitized at each scanning point and is subjected to a realtimeevaluation with the help of digital signal processing and programmablelogic with a time interval shorter than the period. Moreover, in apreferable embodiment the data stream can be forwarded to a furthercomputer unit for online evaluation and for storage for post-processingpurposes.

In the present application the following shall apply:

Realtime evaluation shall be understood as being an evaluation of adigital data stream and the provision of the result(s) within a fixedlypredetermined time interval. If the result of the evaluation is to beused as an actual value for a controller, such a realtime evaluationshall be necessary in order to minimize the controller deviations.Online evaluation shall be understood as being an evaluation of a datastream occurring parallel to the data stream without the necessity ofproviding a result within a predetermined time interval. This isadvantageous when one wishes to make a statement on the success of themeasurement already during a measurement. In this case, a processing ofthe measured data that occurs in parallel is necessary. Post-processingshall be understood in the present application as an evaluation of adata stream previously stored on a data storage medium, such as a harddisk of a computer, without any restrictions concerning the timerequirements.

The digitization of the force-time curve and the evaluation by means ofprogrammable logic allows determining from the force-time curve one orseveral characteristic variables of the force-time curve both inrealtime as well as online according to control necessities as well aswithin the scope of post-processing for each scanning point according todefinition. It is then possible to build up images of the properties ofthe specimen surface from said characteristic variables. By includingthe entire curve in the evaluation instead of individual curve points itis possible, in addition to building up an image with the help ofcharacteristic variables, to also use them for deriving certainquantitative physical properties.

The active production and control of the modulation signal in theinvention, which is in contrast to the classical pulsed-force method,allows influencing the modulation curve shape, phase, amplitude andfrequency, either interactively during the measurement or automaticallycontrolled by control parameters.

As a result, a plurality of methods become applicable by the inventionfor the evaluation of the force-distance curves, which methods allow, incontrast to previous measuring methods, detecting and distinguishingbetween a large variety of specimen parameters within a singlemeasurement such as viscous, adhesive and elastic behavior. Since theforce-distance curves are present in a completely digital form at theend of a measurement and thus can also optionally be subjected to atime-consuming post-processing process, the stored data are alsoavailable for subsequent clarification of measurement artifacts. At thesame time, online evaluation allows a momentary success check at thetime of measurement. In comparison with the “pulsed-force” microscopyaccording to the previously cited state of the art, more comprehensiveevaluation methods can be used.

The possibility appears to be advantageous in that the number ofvariables used for the control and otherwise is no longer subjected toany limitations and the change from one evaluation method to anotheronly needs to be made by software and no longer by the exchange ofhardware as in the state of the art.

Especially preferably, the frequency of the periodic movement of thescanning probe is 1 Hz to 20 kHz in the direction perpendicular to thespecimen surface and the amplitude is in the region of 10 to 500 nm.Advantageously, sinusoidal or sinus-like excitations are chosen. Otherexcitations such as saw-tooth-like or trapezoid can also beadvantageous. An analysis of the actual movement of the scanning probeallows modifying or changing the shape of the excitation in such a waythat the probe performs the desired periodic movement.

The starting point for the image build-up is the determination of thezero line as a characteristic variable. The zero line can vary frompoint to point due to far-reaching electrostatic forces. The zero linecan be determined from the force value of the force-time curve which isobtained when the scanning probe is close to the specimen surface, butis not yet in contact with the same.

All further characteristic variables are obtained from the force-timecurve by taking into account this base or zero line.

In a first embodiment of the invention it can be provided that themaximum repulsive force value is determined as a further characteristicvariable from the digitized force-time curve which is obtained while thescanning probe is in contact with the surface.

It is provided for in a further embodiment of the invention that thedifference between a point in the rising or falling branch of theforce-time curve to the maximum force is designated as a characteristicvariable. This difference is then a quantifiable measure for the localstiffness of the specimen and offers a stiffness image of the surfacewhen entered on the scanned region.

In a further embodiment of the invention it can be provided that theminimum attractive force value on detaching the tip from the specimensurface is determined as a characteristic variable from the force-timecurve. This characteristic variable is a quantifiable measure for thelocal adhesion of the specimen and leads to an adhesion image of thesurface when it is entered over the scanned region.

The minimum force value when snapping the specimen probe onto thespecimen surface can be determined as a further characteristic variablefrom the digitized force-time curve. Said minimum force value is aquantifiable measure for the local attraction of the specimen. If thischaracteristic variable is entered over the scanned region, anattraction image of the specimen can be obtained.

Stiffness images of the specimen can also be determined in anothermanner from the recorded force-time curve. In a first embodiment, astiffness image is obtained in such a way that the slope of theforce-time curve at a certain time when pressing the specimen probe intothe specimen surface is determined as a characteristic variable. Thisslope is a quantifiable measure for the local stiffness of the specimen.

As an alternative to this, the slope can be determined at a specificrelative time of the force-time curve when the specimen probe is pulledaway from the specimen. This slope is also a quantifiable measure forthe local stiffness of the probe and leads to a stiffness image of thesame when entered over the scanned region.

It may be provided for in a further embodiment of the invention that thefrequency of the free oscillation of the cantilever is detected as thecharacteristic variable. This is a quantifiable measure for thecollected impurities or damage to the tip.

The ratio between the minimum force value when detaching from thespecimen surface and the measured force value on the first followinglocal force maximum can be determined as a further characteristicvariable. This characteristic variable is a quantifiable measure for theenergy dissipation when detaching the tip from the specimen.

When one determines from the force-time curve the rise time from thebeginning of the contact up to the maximum force, it is possible togenerate a rise time image of the specimen surface. It is analogouslypossible to obtain a fall time image of the specimen surface bydetermining the fall time from the digitized force-time curve.

In a further development of the invention it may be provided that thetime of the repulsive contact between specimen and tip or the time ofcontact between specimen and tip is determined from the digitizedforce-time curve which is also recorded. When entered over the scannedregion, these times lead to a repulsive contact image or a contact timeimage of the specimen surface.

Similar to the contact periods in the repulsive region of the forcecurve, contact periods for the adhesive portion of the force curve,e.g., from the force minimum to the zero crossing of the force curve,can be determined in a further development of the invention.

When entered on the scanned region, these periods lead to acontact-breaking period image of the specimen surface.

In addition to the direct evaluation of the force-time curve, it ispossible to determine various integrals under the force-time curve ascharacteristic variables. For example, it is possible on the basis ofthe digitized curve to determine the integral under the force-time curvein the region of the repulsive contact or from the beginning of thecontact until reaching the maximum force and from reaching the maximumforce until the zero crossing of the force. When entered over thescanned region, these integral values offer a repulsive contact integralimage of the specimen; in the case of the integral from the beginning ofthe contact until reaching the maximum force, an image of the workprovided on the specimen and in the case of the integral from the timeof reaching the maximum force until the zero crossing, an image of thework provided by the specimen.

Similar to the integrals in the repulsive region, integrals for theadhesive region of the force curve can also be determined from thedigitized force-time curves.

It is possible for example to determine the surface area under the forcecurve from the time of minimum force up to the time of zero crossing ofthe force curve.

This integral is a measure for the local elastic-viscous properties ofthe specimen.

When calculating the difference of the integrals in the region of therepulsive contact and the integral under the force-time curve from thebeginning of the contact until reaching the maximum force, an image canbe produced of the work dissipated in the specimen.

It is particularly advantageous when the characteristic variablesdetermined from the force-time curve are stored in a second memory areaby allocating the various measuring and scanning points.

As a result of realtime evaluation, the invention allows obtaining astatement very rapidly for the very first time as to whether or not themomentarily performed measurement is occurring successfully because thedigitized force-time curve which is evaluated in realtime is availableto the user either immediately, i.e., during the running measurement asan electric signal which can be tapped externally from the device andcan thus be read in by any kind of AFM controller, or visualized by thecontrol computer.

In addition to the method in accordance with the invention, theinvention also provides an apparatus for performing the method, with thescanning probe microscope for performing the method being characterizedin that the apparatus comprises an analog-to-digital converter in orderto digitize the recorded force-time curve and in order to enable thedetermination of predetermined characteristic variables from thedigitized force-time curve in realtime.

One or several of the obtained realtime evaluation results can be usedas a control signal for tracking the scanning probe on the specimentopography or for controlling the modulation signal. Preferably, thedifference between the maximum repulsive force value and the force valueobtained when the scanning probe is close to but not in contact with thespecimen is used as the control signal for tracking the scanning probeon the specimen topography. It is advantageously also possible to useother variables.

If the digitized force-time curves are stored in a memory area, certainvariables of the force-time curve can be determined by post-processing.

The oscillating movement of the scanning probe perpendicular to thespecimen surface is excited with the help of a piezoelectric element.

Furthermore, it is provided for in a first embodiment that the scanningprobe comprises a tip arranged on a beam and the means for recording theforce-time curve comprise means for measuring the beam deflection, e.g.with the help of the deflection of a laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is to be described below by way of examples shown in thedrawings, wherein:

FIG. 1 shows a characteristic curve of a force-time curve.

FIG. 2 shows a block diagram of a scanning probe microscope inaccordance with the invention.

FIG. 3 shows a block diagram of a scanning probe microscope with aprogrammable logic device.

FIG. 4 shows an alternative system with a programmable logic device.

DETAILED DESCRIPTION

FIG. 1 shows the characteristic progress of a force-time curve asobtained after passing through an oscillation period of a scanningprobe, which in the present case is a probe tip arranged on a beam. Theoscillation amplitude of the oscillation of the scanning probe tip asexcited by means of a piezoelectric element lies between 10 and 500 nmand the oscillation frequency between 1 Hz and 5 kHz, and in the presentcase in the region of 1 kHz.

FIG. 1 clearly shows the characteristic regions of the force-time curvewhich arises, when excited, perpendicular to the specimen surface. Saidregions can be used for determining the characteristic variables and,when applied to the scanned region, lead to the different forms of imageof the specimen surface.

The function as illustrated in FIG. 1 is already standardized on thebase or zero line, which means that the force value of the base line ofthe scanning probe is set to zero. The base line can be determined insuch a way that the region of the force-time curve is determined inwhich the force value no longer changes. This value, which is providedwith the reference numeral 5 in this case, is set to zero. Relative tothis, one determines the other force values of the curve.

The scanning probe is moved towards the specimen surface at first. Afterapproximately 0.2 milliseconds the probe comes into contact with thespecimen due to the negative attractive forces between scanning probeand specimen. Once the tip is in contact with the specimen, force iscontinued to be exerted by the piezoelectric element on the scanningprobe or the tip and the tip is thus driven into the specimen orspecimen surface. The repelling repulsive forces increase strongly andreach a maximum at point 3. After a preset path or a preset maximumforce value F_(max), the scanning probe is no longer driven into thespecimen but pulled back by the piezoelectric element from the specimen.Due to the adhesive forces, it comes out of contact with the specimenonly after reaching the force minimum at point 4 and passes over into afree oscillation. The free oscillation decays until the base line 5 isreached.

The cycle is then repeated again.

The progress of the force-time curve is principally the same for allspecimens which are examined with the help of the “pulsed-forcemicroscopy”. However, it is possible to determine characteristicvariables from the curve for the respective specimen or for therespective point of the probe, which variables, when composed, lead toan image of the specimen surface depending on the various physicalparameters.

As a result, the difference between point 2 in the ascending branch ofthe force-time curve and the maximum force is a quantifiable measure forthe local stiffness of the specimen. When this characteristic variableis evaluated from the recorded force-time curve according to theinvention, one can thus obtain a local stiffness image of the specimen.

The minimum attractive force value 4 when detaching the tip from thespecimen surface is again a quantifiable measure for the local adhesionof the specimen and offers an adhesion image when applied to the scannedregion.

The minimum force value when latching the scanning probe onto thespecimen surface in point 1 is a quantifiable measure to the localattraction of the specimen and leads to an attraction image of thesurface when applied to the scanned region. From the rise times from thestart of the contact until the maximum force and the fall time from themaximum force until reaching the zero crossing lead to rise and falltime images of the specimen surface.

The invention also allows evaluating integral variables. As a result,the integral under the force-time curve can be determined in the regionof the repulsive contact and the integral under the force-time curvefrom the start of the contact until reaching the maximum force in point3. If these two integral values are deducted from each other, oneobtains a quantifiable statement on the work dissipated in the specimen.

FIG. 2 shows by way of an example a block diagram of the configurationof a scanning probe microscope in accordance with the invention which isoperated in “pulsed force mode.” The scanning probe microscope isdesignated with reference numeral 100. The scanning probe microscopecomprises a scanning probe 102 which is usually a tip. The scanningprobe is suspended on a beam 104. The scanning probe is made tooscillate in the z direction 106, i.e. in the perpendicular directionrelative to the specimen surface. The deflection of the beam 104 onwhich the tip 102 is arranged is evaluated by a beam which is emitted bya laser diode 108 and is detected by a four-quadrant detector 110. Theanalog force measurement signal which is obtained by the deflection ofthe beam 104 which is also designated as cantilever is provided withreference numeral 120. The analog force signal 120 is supplied to acontrol unit 122 according to the invention. The control unit 122comprises an analog-to-digital converter 124 which converts the analogdata of the force signal 120 into a digital data stream 126. The digitaldata stream is evaluated by means of a realtime evaluating unit 128 inrealtime by means of programmable logic unit for example. Realtime shallbe understood in such a way that the result of the evaluation isobtained in a guaranteed fashion within a fixedly predeterminedinterval, i.e. in this case not later than until the end of the currentmodulation cycle, so that the result can be used as an actual value fora controller. The programmable logic unit can be realized by “fieldprogrammable gate arrays” (so-called FPGAs) for example. Suchprogrammable logic units have been described for example in Ashok K.Sharma: “Programmable Logic Handbook: PLDs, CPLDs and FPGAs (McGraw-HillProfessional Publishing; ISBN: 0070578524)” or in “W. Bolton, BillBolton: Programmable Logic Controllers: An Introduction(Butterworth-Heinemann; ISBN: 0750647469)”.

With the help of realtime evaluation 128 it is possible, once theevaluated digital signal had been converted back into an analog signalagain in the digital-to-analog converter 130, to use for controllingpurposes the constant maximum force (by taking into accountinterferences or measuring artifacts caused by far-reaching forces), theconstant energy introduction, constant penetration depth, etc., orcombinations of such variables.

An external analog signal such as a set-point value predetermined by theAFM controller can also be included by the analog-to-digital converter130 in the calculation of the actual value for the controller. Thecontrol variables are sent by the controller of the scanning probemicroscope 134 to the scanning probe microscope 100 for tracking the tip102 on the beam 104.

It is the task of the modulator 131 to produce the vertical oscillationof the measuring tip which is necessary for “pulsed force mode”. Thedigital configuration allows using any desired shape of curve for themodulation. By providing a close linkage to the aforementioned realtimeevaluation, it is possible to have an influence which is automaticallycontrolled by control parameters on phase, amplitude and frequency ofthe modulation in addition to an interactive intervention by the user.This allows the correction of piezoelectric non-linearities of thescanning probe microscope.

In addition to realtime control or tracking of the scanning probe 104,the realtime evaluation with the help of the module 128 also allows thesynchronous evaluation of characteristic data in the module 140 and thusan online check or evaluation 142 of the measurement. Furthermore, amemory area 144 can be provided to which the digital data stream can besaved. The data stream 144 saved to the memory can be executed offlinein a post-processing process 146 after the measurement has beencompleted.

By way of example, FIG. 3 shows a block diagram of the configuration ofa scanning probe microscope in accordance with the invention with aprogrammable logic device. The scanning probe microscope is indicated byreference numeral 1100. The scanning probe microscope comprises ascanning probe 1102, which is for instance a tip. The scanning probe issuspended on a beam 1104. The scanning probe is set in motion tooscillate along the z axis 1106, i.e., perpendicular to the samplesurface. The deflection of the beam 1104 on which the tip 1102 isarranged is evaluated by means of a reflected beam emitted by a laserdiode 1108 that is detected by a four-quadrant detector 1110. The analogforce measurement signal which is obtained by the deflection of the beam1104, also known as a cantilever, is indicated by reference numeral1120. The analog force signal 1120 is transmitted to a control unit 1122in accordance with the invention. The control unit 1122 comprises an A/Dconverter 1124 which converts the analog data of the force signal 1120Into a digital data stream 1128. The digital data stream is communicatedto a programmable logic device, developed here as an FPGA, without theinterconnection of a bus system. The embodiment only shows an A/Dconverter 1124. This is a simplified representation. Provision is madefor at least four A/D converters in preferred systems, namely one eachfor the x-axis and the y-axis that characterize the plane on which thescanning platform with the sample 1150 is displaced beneath the scanningprobe 1102, and also an A/D converter for the Z axis. Consequently, inthe form of a digital data stream, these 3 A/D converters serve toprovide the position of the scanning platform in all three dimensions tothe programmable logic device 1160, developed as a field programmablegate array (FPGA). In addition, provision is made for one or a pluralityof A/D converters to receive the measurement signal, in this case theforce-time signal. The digital data stream of the A/D converters is fedto the programmable logic device 1160 in parallel, and thereforesimultaneously, being processed simultaneously by this device.Preferably, the A/D converters have a width of 14 bit or more. With theaid of the programmable logic device, the realtime A/D converter signalsare evaluated in real time. Realtime is defined such that the result ofthe evaluation is definitely available for the tip 1102 within a fixedpredetermined interval, in this case no later than the end of thecurrent modulation cycle, so that the result can be used as an actualvalue for a controller. The closed loop control is performed by acontroller, that in turn constitutes one component of the fieldprogrammable gate array (FPGA). The programmable logic device 1160(FPGA) directly controls one D/A converter or a plurality of D/Aconverters without the interconnection of a data bus. Preferably, theD/A converters 1130 are those with a width of 14 bit or more.Preferably, provision is made in the scanning probe microscope inaccordance with the invention with programmable logic for at least threeD/A converters, specifically in order to displace the sample along theX, Y and Z axes in the three dimensions. The programmable logic devicecan for instance be developed as field programmable gate arrays(so-called FPGAs). Such programmable logic devices have been describedfor example in:

-   -   Ashok K. Sharma: “Programmable Logic Handbook: PLDs, CPLDs and        FPGAs (McGraw-Hill Professional Publishing; ISBN: 0070578524)”        or in:    -   W. Bolton, Bill Bolton: “Programmable Logic Controllers: An        Introduction” (Butterworth-Heinemann; ISBN: 0750647469).

When a control variable of a scanning probe microscope in pulsed forcemode is described, the following values can be taken into considerationfor instance for closed-loop control purposes; the constant maximumforce (taking measurement artifacts resulting for instance frominterference or long-range forces into account), the constant energyinput, the constant insertion depth etc., or combinations of thesequantities.

The actual controller quantity is calculated in the programmable logicdevice, The control variables from the programmable logic device aretransmitted without the interconnection of a data bus to one or aplurality of D/A converters 1130, for instance to transport the samplingplatform in the three spatial dimensions, or to a modulator 1131 tomodulate the amplitude, phase and frequency of the tip 1102 of thescanning probe microscope 1100. Thanks to the architecture of theprogrammable logic device 1160, the D/A converter and the modulator canbe controlled in parallel mode. The programmable logic device 1160 ofthe system shown in FIG. 3 is connected to at least three peripheralcomponents 1124, 1130, 1131.

The modulator 1131 makes it possible to control the vertical oscillationof the measurement tip in pulsed force mode. The digital configurationmakes it possible to employ any number of curve forms for modulation. Inaddition to interactive user access, the close connection to therealtime evaluation described above also makes it possible by means ofcontrol parameters to automatically control the phase, amplitude andfrequency of modulation, permitting for example the correction of piezonon-linearities In the scanning probe microscope.

In addition to realtime control, real time evaluation employing theprogrammable logic device 1160 makes it possible to store some of thedata in a memory in the programmable logic device. The data in thememory area 1140 can be subjected to post-processing 1142 or filtering.An external computer 1164 can be connected to the programmable logicdevice by means of an interface, for instance a USB interface 1162,which in turn is linked directly to the programmable logic device 1160.The external computer serves to input the measurement and controlvariables and also to act as a storage medium for measurement data.Within the scope of this application, the USB interface is a peripheralcomponent.

FIG. 4 is a detailed embodiment of a scanning probe microscope with aprogrammable logic device represented in accordance with the invention.The same components as in FIG. 3 have reference numbers that are greaterby 100. In the embodiment in accordance with FIG. 4, in addition to theprogrammable logic device recording and evaluating the measured values,the movement of the sample or scanning platform in all three spatialdimensions is controlled, as is the oscillation of the peak force of thescanning probe microscope.

The three A/D converters 1224.1, 1224.2 and 1224.3 connected to theprogrammable logic device for receiving the position of the scanningplatform via the X, Y and Z sensors 1225 are easily recognizable. Thefeedback data for controlling scanning are provided by means of the D/Aconverters 1230.1, 1230.2 and 1230.3 and transmitted to the controller.The central processing unit embedded in the programmable logic devicegenerates the signal for the modulator 1231 used to control themodulation of the force tip 1202 via the digital output 1232.Furthermore, the four-quadrant detector 1210 of the scanning probemicroscope is connected with the programmable logic device 1260. Thefour-quadrant detector 1210 receives a left/right signal via inputTB/ADC 1242 or LR/ADC 1244. These signals are processed in theprogrammable logic device and fed to a lock-in amplifier 1246 orcontroller 1248 which is also developed in the programmable logicdevice. The scanning platform is controlled by the controller 1248 viathe digital outputs 1230.1, 1230.2 and 1230.3 and moved into thecorresponding position. The force tip 1202 is actuated by means of thesinus generator or modulator 1231 via the output 1232. Furthermore, theprogrammable logic device 1260 comprises a digital filter 1250 for therecorded data and areas 1252, 1253 for collecting and storing theavailable data. The programmable logic device can also optionally beconnected to auxiliary A/D converters, i.e., Aux/ADC 1254.1 and Aux/DAC1254.2, and digital input and output devices 1254.3. The data stored inthe data storage device 1252 can be transmitted via a computer interface1256 or a USB interface to an external computer 1258 and stored there.The computer 1258 can also serve to set the measurement parameters etc.In accordance with the invention, as a peripheral component theinterface 1256 is connected directly to the programmable logic device1260.

Consequently, the invention also makes known for the first time anapparatus that makes it possible to execute a plurality of parallelinput/output operations in the peripheral component directly withoutinterconnection of data busses to a programmable logic device. Theprogrammable logic device encompasses not only a means for evaluatingthe data provided in digital form, but also for instance for controllingthe input/output interfaces and the closed-loop control of the sampleplatform that can be displaced along the X, Y and Z axes, and also foractuating the “field tip.”

The configuration of the programmable logic device as presented in theinvention, which controls A/D converters, D/A converters and digital I/Oconnections and encompasses controllers or lock-in amplifiers, can beemployed not only in scanning probe microscopes, but also generally inother measurement devices, also in particular in microscopes, especiallyin scanning measurement systems, such as scanning force microscopes,scanning tunneling microscopes, optical near-field microscopes, confocallaser scanning microscopes, confocal scanning microscopes, confocalRaman scanning microscopes and photonic force microscopes.

The invention thus provides a method and an apparatus for the first timefor performing a method which allows precisely determining a largenumber of variables which are characteristic for a specimen by means ofa single measurement and obtaining therefrom the imaging of differentphysical surface properties.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A microscope, comprising a programmable logic device that includes field programmable gate arrays (FPGAs).
 2. A microscope according to claim 1, wherein the microscope includes a scanning microscope.
 3. A microscope according to claim 1, wherein said scanning microscope is a microscope selected from the group of microscopes comprising: a scanning force microscope, a scanning tunneling microscope, a near-field scanning optical microscope, a confocal Raman scanning microscope, a photonic force microscope, a scanning electron microscope and a laser scanning microscope.
 4. A microscope, comprising: a first programmable logic device comprising multiple logic components interconnected using a netlist and freely configurable circuits in accordance with a circuit diagram, wherein the first programmable logic device includes a field programmable gate array (FPGA) configured to provide: a real time evaluation, a controller, a memory, a filter, and a post processor.
 5. A microscope according to claim 4, wherein the microscope further comprises a peripheral electrical component connected to the first programmable logic device without using a data bus interconnection.
 6. A microscope according to claim 4, wherein the microscope comprises at least two peripheral components, with the at least two peripheral components being connected directly to the first programmable logic device without using a data bus interconnection
 7. A microscope according to claim 5, wherein the first programmable logic device controls the peripheral component directly.
 8. A microscope according to claim 6, wherein the first programmable logic device controls the at least two peripheral components directly.
 9. A microscope according to claim 4, including peripheral components that comprise one or more of the following components: an analog-to-digital (A/D) converter; a digital-to-analog (D/A) converter; a digital input and output (DIO); a digital signal processor (DSP); a microprocessor; and a second programmable logic device.
 10. A microscope according to claim 9, wherein the A/D converter has at least one of a) a width equal to or greater than 14 bits and b) a sampling rate in excess of 100 ksamples/s.
 11. A microscope according to claim 4, wherein the microscope comprises a digital-to-analog (D/A) converter having at least one of a) a width equal to or greater than 14 bits and b) a sampling rate greater than 100 ksamples/s.
 12. A microscope according to claim 9, wherein the DIO includes one of the following interfaces: a RS232 interface; a 12C interface; an Ethernet interface; and a USB interface.
 13. A microscope according to claim 9, wherein the DIO comprises a control interface for one or more of the following components: a filter disk; a filter slider; a laser illumination unit; an electric rotary table drive; a spectrometer; a spectrograph; a CCD camera; and an interface for controlling a scanning system and inputting data therefrom
 14. A microscope according to claim 9, wherein the DIO comprises one or more of the following: a digital output unit that can control stepper motors; a digital output unit that can control folding mirrors; a digital output unit that can control shutters or acousto-optic modulators; a digital output unit that can switch detectors or their functions on and/or off as a function of a measured counting rate.
 15. A microscope according to claim 4, wherein the microscope comprises at least first and second peripheral components, with the first peripheral component including an A/D converter that receives a measurement signal and that provides a digital measurement data stream.
 16. A microscope according to claim 15, wherein the second peripheral component includes a D/A converter that provides an analog signal to control the microscope.
 17. A microscope according to claim 13, wherein the first programmable logic device encompasses an evaluation area that evaluates a first data stream from a first peripheral component.
 18. A microscope according to claim 17, wherein the first programmable logic device encompasses a control area that obtains a second data stream made available to a second peripheral component.
 19. A microscope according to claim 18, including a second peripheral component comprising a digital-to-analog (D/A) converter configured for a positioning device that is adapted to position and scan a sample in one, two or three dimensions.
 20. A microscope according to claim 4, wherein the first programmable logic device is configured to parallel process simultaneously occurring processes.
 21. A microscope according to claim 4, wherein the microscope comprises a scanning microscope.
 22. A microscope according to claim 21, wherein the scanning microscope comprises at least one scanning microscope selected from the group of scanning microscopes comprising: a scanning force microscope, a scanning tunnelling microscope, a laser scanning microscope, a photonic force microscope, a near field scanning optical microscope, a scanning electron microscope, and a confocal Raman scanning microscope.
 23. A microscope according to claim 9, wherein the A/D converter has a width equal to or greater than 16 bits and a sampling rate in excess of 5 Msamples/s.
 24. A microscope according to claim 11, wherein the A/D converter has a width equal to or greater than 16 bits and a sampling rate in excess of 5 Msamples/s. 